Guide wires are used to guide catheters for use in the treatment of body regions that are difficult to operate on surgically, the treatment of body regions through minimally invasive surgery, and the inspection of blood vessels by cardiac angiography. For example, to perform PCI (Percutaneous Coronary Intervention) under X-ray radioscopy, the distal end of a guide wire is placed to project from the distal end of a balloon catheter, and the guide wire together with the balloon catheter is inserted into the blood vessel up to a position near the constricted area of the coronary artery in question for guiding the distal end of the balloon catheter to the position near the constricted area.
An example of a guide wire used in the above treatment is disclosed in U.S. Pat. No. 5,797,857. The disclosed guide wire includes a flexible wire body (core), a coil (a metal coil for X-ray angiography) disposed in surrounding relation to the distal end of the wire body, and a covering layer (a covering member of synthetic resin, a hydrophilic lubricating layer) covering the outermost surfaces of the wire body and the coil.
When the guide wire disclosed in U.S. Pat. No. 5,797,857 is used to guide the catheter as described above, the following phenomena tend to occur depending on the state of the coronary artery such as the degree of curvature of the coronary artery:
If the guide wire is pushed in when the coil of the guide wire reaches (is inserted into) a sharp bend of the coronary artery, for example, undue forces (tending to cause a plastic deformation) are liable to be applied to the coil. At this time, a turn of the wire of the coil rides onto an adjacent turn of the wire, thus tending to plastically deform the coil. Therefore, the coil will not recover its ordinary (normal) state, and the pushing force applied from the proximal end of the wire body will not be reliably transmitted to the distal end of the wire body, i.e., the guide wire pushing capability is greatly reduced.
Though the coil of the guide wire disclosed in U.S. Pat. No. 5,797,857 has the hydrophilic lubricating layer, a relatively large frictional resistance is developed between the hydrophilic lubricating layer and a sharp bend of the coronary artery depending on the thickness of the guide wire when the coil of the guide wire reaches (is inserted into) the sharp bend of the coronary artery. Therefore, the torque from the proximal end of the guide wire is not reliably transmitted through the coil to the distal end of the wire body, i.e., the torque transmitting capability is greatly reduced.